1. Field of the Invention
The present invention relates to an image analysis method for determining the interior points of an object in a background. The present invention also relates to a method of identifying at least one valid object having at least one predetermined attribute value in a background. By determining the interior points of the object, one may "blacken out" or effectively remove previously identified objects from an image of the object and the background, thus creating a remainder image for further searching.
2. Description of the Related Art
The ability to access interior points of a region when its contour is given is a classic problem in image processing. Previous solutions to this problem have been described by L. W. Chang and K. L. Leu in an article entitled "A Fast Algorithm for the Restoration of Images Based on Chain Codes Description and Its Applications", Computer Vision, Graphics, and Image Processing 50, 296- 307 (1990). One algorithm described, connectivity filling, requires that every pixel in the object be interrogated. Since the number of pixels within an object is greater than the number of pixels which comprise the perimeter of the object, such a technique is relatively slow. Another method described is parity checking which is based on the fact that the intersection of a straight line with the contour regions of an object delineates an even number of points on the perimeter of the object. Designation of the interior points is determined by an arbitrary filling rule where all points between each odd point and the next even point on the contour in each line of the image are designated as interior points. Such a parity checking algorithm will not work with objects of complex shape.
In the same article cited above, Chang and Leu propose an enhanced parity checking algorithm which relies on characterizing the perimeter points into one of four categories based on direction code values. Characterizing the points leads to the creation of a new buffer of perimeter points wherein some points have been duplicated and others eliminated. By applying the parity checking algorithm to the newly created buffer, interior points of objects with complex shapes may be identified. However, the enhanced algorithm presented by Chang and Leu is an indirect method for solving the problem of interior point determination, requiring an excessive number of steps.
Japanese Patent Publication Number 62-60069 to Hitachi Electronic Engineering Co. Ltd., published Dec. 14, 1987, discloses a colony screening device which distinguishes colonies based on color. Colonies are identified by pattern recognition using a predetermined threshold and a small number of points in the center of a colony are arbitrarily selected. This publication does not disclose a method for determining all the interior points of an object. Limiting the area of determination introduces possibilities of error into any attempt at object identification and makes a search of the remainder portion of the image less effective.
U.S. Pat. No. 4,453,266 to Bacus discloses a method for measuring the optical density of a cell using the sum of gray level values within the closed boundaries of the cell. Bacus does not contemplate determining all of the interior points of an object of an unknown or arbitrary shape using an automatic thresholding technique.
None of these references discloses a method for determining all the interior points of the object identified. Furthermore, none of these references discloses a method of identifying at least one valid object having at least one valid object predetermined attribute value in a background using automatically calculated thresholds by determining the interior points of the object. Moreover, none of these references discloses a method for effectively removing previously identified object from an image, thereby creating a remainder image for further searching.